Activation of Ni2V2O7 to nonstoichiometric NiV3O8 for solar-driven photoelectrochemical water oxidation

Hydrogen treatment is an effective strategy to introduce non-stoichiometry and improve the performance of semiconductor nanomaterials for photocatalytic applications. Herein, for the first time, we report the hydrogen treatment activation of non-photoactive nickel vanadate (NV) towards photoelectrochemical (PEC) water oxidation. The NV nanostructures are synthesized by a sonication-assisted hydrothermal method. Hydrogentreated nickel vanadate (H-NV) nanoflakes were achieved by subjecting the NV to anneal at 350 degrees C for 4 h in a hydrogen atmosphere. Field emission scanning electron microscopy (FESEM), and High resolution transmission electron microscopy (HRTEM) indicates irregular network morphology for the as-synthesized NV nanostructures, calcined at 500 degrees C (NV-500). The XRD pattern confirms monoclinic and orthorhombic crystal phases for NV-500 and hydrogen treated nickel vanadate (H-NV-500), respectively. The defects states produced on the surface of NV-500 after high dose of electrons which implies the creation of oxygen vacancies and consistent with the XPS analysis for H-NV-500. The optical properties of H-NV-500 via UV-Vis/DRS show significant absorption in the visible regime at lambda = 628 nm with an indirect bandgap value of 2.15 eV from Tauc's plot and supports by density functional theory (DFT) studies. The PEC water oxidation performance has onset potential at similar to 0.74 V. The photocurrent density at saturation is similar to 2.13 mu A/cm(2) for H-NV-500 photoanode. These results suggest that hydrogen treatment effectively activated NV towards PEC water oxidation process, which was initially inactive.

Automated summary

Hydrogen treatment activates non-photoactive nickel vanadate towards photoelectrochemical water oxidation, showing significant absorption in the visible regime and achieving an indirect bandgap value of 2.15 eV. The hydrogen-treated H-NV-500 photoanode exhibits an onset potential at around 0.74 V and a photocurrent density at saturation of about 2.13 mu A/cm(2).